A camera has a field of view of 87.5° and focal length of 145mm. What is the dimension of the square format?
\[
\alpha = 2\arctan\frac{d}{2f}
\]
\[
87.5^{\circ} = 2\arctan\frac{d}{2(145mm.)}
\]
\[
d = 277.61460525389mm.
\]
\[
d = a \sqrt 2
\]
\[
277.61460525389mm. = a \sqrt 2
\]
\[
a = 196.30316993145mm.
\]
\[
a \approx 196.30mm. \leftarrow \text{answer}
\]